MESOSCALE PRECIPITATION DISCUSSION 0131
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
734 PM EDT SUN MAY 06 2018

AREAS AFFECTED...NORTHERN ID...WESTERN MT

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 062335Z - 070235Z

SUMMARY...SCATTERED CONVECTION PRODUCING LOCALLY HEAVY RAINFALL
OVER AREAS EXPERIENCING SNOWMELT COULD POSE A FLASH FLOOD THREAT
INTO THE EARLY EVENING HOURS.

DISCUSSION...REGIONAL RADARS SHOWED AN INCREASING AREA OF
SCATTERED CONVECTION EXTENDING FROM NORTHEAST OR ACROSS NORTH
CENTRAL ID INTO SOUTHWESTERN MT THIS AFTERNOON. THE GOES-16 CLEAN
IR LOOP HAS SHOWN STEADILY COOLING TOPS WITH THE CONVECTION FROM
NORTH CENTRAL ID INTO WESTERN MT...WITH CLOUD TOPS TEMPERATURES
NEAR -65 CELSIUS.

THE CONVECTION WAS FORMING IN AN AREA OF 500-1000 J/KG OF MLCAPE
(WITH SOME LOW LEVEL CIN STILL IN PLACE)...WITHIN AN AXIS OF
0.75/1.00 INCH PRECIPITABLE WATER AIR (WHICH IS ABOUT TWO STANDARD
DEVIATIONS ABOVE THE MEAN) EXTENDING FROM SOUTH CENTRAL WA INTO
SOUTHWEST MT. STEEPENING MID LEVEL LAPSE RATES AHEAD OF A SHORT
WAVE OVER NORTHEAST OR HAS RESULTED IN HAIL BEING THE PRIMARY
CONVECTIVE MODE THUS FAR...EVEN THOUGH KMSX RADAR SHOWED HOURLY
RAINFALL RATES NEAR 0.80 INCHES OVER NORTH CENTRAL ID.

AS THE SHORT WAVE SLOWLY CROSSES NORTHEAST OR AND SOUTHEAST WA
THIS EVENING... INCREASING DIVERGENCE SHOULD PROVIDE SUFFICIENT
SYNOPTIC SCALE ASCENT TO PROMOTE FURTHER CONVECTIVE DEVELOPMENT.
RAP SOUNDINGS SHOWED 500-1000 J/KG OF MLCAPE REMAINING IN PLACE
OVER NORTHERN AND CENTRAL ID/WESTERN MT THROUGH AT LEAST 07/03Z.
HOWEVER...THESE SOUNDINGS ALSO SHOWED LOW LEVEL CIN RETURNING BY
THAT TIME...CAUSING THE CONVECTION TO BECOME ELEVATED.

BEFORE 07/03Z...CONVECTION TRACKING FROM SOUTHWEST TO NORTHEAST IS
EXPECTED TO MOVE OVER AREAS WITH SNOWMELT OCCURRING. HOURLY
RAINFALL RATES THROUGH 07/03Z COULD APPROACH 1.00 INCHES...AND ANY
TRAINING IN THE QUASI UNIDIRECTIONAL FLOW IN THE MID LEVELS COULD
RESULT IN LOCAL 2.00 INCH RAINFALL AMOUNTS. THE 18Z HREF MEAN
SHOWED A 50 TO 70 PERCENT PROBABILITY OF 2.00 INCHES OVER NORTH
CENTRAL ID THROUGH 07/04Z.

LOCAL RAINFALL AMOUNTS THIS HIGH COULD POSE A FLASH FLOOD
THREAT...AS THE SNOWMELT HAS RESULTED IN ONE AND THREE HOUR FLASH
FLOOD VALUES OF LESS THAN AN INCH OVER NORTHERN ID INTO A PORTION
OF WESTERN MT. HEAVY RAINFALL IN THESE AREAS COULD RESULT IN FLASH
FLOODING...OR AN EXACERBATION OF ONGOING FLOODING.

THE OVERALL CONVECTIVE COVERAGE IN EXPECTED TO BEING DIMINISHING
AFTER 07/03Z...WHEN LOW LEVEL CIN INCREASES...AND THE INSTABILITY
BECOMES MORE ELEVATED.

HAYES

ATTN...WFO...MSO...OTX...TFX...

ATTN...RFC...MBRFC...NWRFC...

LAT...LON   48411391 47161244 46351238 45841343 45761477
            45871669 46541715 47291710 48091636